January 17, 2021 – Above normal temperatures and dry conditions are forecast to prevail again today. Strong winds will develop Sunday night and into Monday morning. Even stronger winds are possible Monday night and into Tuesday. Temperatures will gradually cool through the week with a chance of light precipitation returning late week.
GOES-West infrared satellite imagery reveals just a few high clouds drifting overhead interior northern California this early morning. Not much of any fog has thus far been detected as of 2 AM PST; the only signs of marginally-reduced visibilities are in the northern San Joaquin Valley around Stockton and Modesto.
Farther to the north, a few weather stations are beginning to report some gusty northerly winds, particularly around Red Bluff and in the foothills of Butte and Tehama Counties. This mixing will prohibit any opportunity for fog development in the northern Sacramento Valley.
The dominate upper level ridge remains parked off the California coast, and has been responsible for the prolonged spell of dry conditions and above normal temperatures.
Temperatures from yesterday will repeat again today with highs in the upper 60s to upper 70s in the Sacramento and northern San Joaquin Valleys, or about 12 to 24 deg F above normal. Yesterday’s 71 deg F high in Downtown Sacramento ties for the 3rd earliest recorded >= 70 deg F day with records going back to 1877. The earliest >= 70 deg F day on record for Sacramento was on January 6, 1911.
Now, attention turns to the impactful wind event that will get underway overnight Sunday as a dry, shortwave trough drops southeastward and parallels the California coast.
Strengthening offshore surface pressure gradients will result in the initial increase of north to east winds across much of the forecast area. Winds will remain strong and gusty into mid-day Monday with the strongest winds impacting the west side of the Sacramento Valley, as well as the Sierra Nevada and adjacent foothills. The 3-km NAM suggests that winds may briefly diminish Monday afternoon through about sunset.
A second shortwave will will further reinforce the offshore flow as it digs south from eastern Washington toward the central/southern Sierra Nevada. Consequently, even stronger winds are likely Monday night and into Tuesday, most notably along the Sierra Crest where the strongest winds are possible. With winds at 500 mb howling over 120 kt, can’t rule out an isolated anemometer along the exposed Sierra crest making a run at 100+ mph gusts. More common wind gusts in the mountains will be in the 50 to 80 mph range.
For the Valley, expect gusts around 40 to 50 mph. After collaboration with neighboring NWS offices, opted to maintain the present High Wind Watch out, which begins Sunday night.
Winds will gradually subside through the day on Tuesday, and continue the decline on Tuesday night. Over the course the first half of the week, temperatures will gradually cool with highs returning the low/mid 60s in the Valley by Wednesday.
Chance of precipitation from now through Wednesday will remain at/below 15 percent for much of the region.
Extended discussion (Thursday through Sunday)
Upper low drops slowly south through interior NorCal Friday into Saturday bringing light precipitation, mainly over the northern and eastern foothills and mountains.
Dry Saturday night into early Sunday as weak short wave upper ridging moves through. Another short wave trough then progged to drop into the area by Sunday afternoon/evening.
Forecast details become more unclear at this point as models differ significantly with strength of wave and overall QPF.